that's been president obama. governor romney hasn't. >> reporter: during the primaries romney demonstrated he can stumble. as he did trying to bet rick perry big money at one debate. >> rick, i'll tell you what, $10,000? $10,000 bet? >> reporter: but romney is no debate lightweight here taking down newt gingrich's idea for a moon colony in florida. >> if i had a business executive come to me and say they wanted to spend a few hundred billion dollars to put a colony on the moon, i'd say you're fired. >> reporter: while romney stays behind closed doors, he's fine tuning his message softening his position on immigration. allowing the children of undocumented workers to stay in the country until immigration reform is passed. he's also out with a tough new ad linking president obama to former house speaker nancy pelosi. >> who will raise taxes on the middle class? barack obama and the liberals already have. >> reporter: fresh ammunition for tomorrow night's debate at an event earlier today in charlotte, north carolina